Electronic devices such as an OLED display, which are thin, excellent in moving picture display performance, and low in power consumption, are used for applications such as a display for a portable phone.
A glass sheet is widely used as a substrate for an OLED display. A glass sheet used for this application needs to have the following main characteristics.    (1) To be substantially free of alkali metal oxides in order to prevent alkali ions from diffusing in a semiconductor film formed in a heat treatment process.    (2) To be excellent in productivity and be excellent particularly in devitrification resistance and meltability in order to produce a glass sheet at low cost.    (3) To have a high strain point in order to reduce heat shrinkage of a glass sheet in a low temperature poly silicon (LTPS) process.
Meanwhile, the OLED display is mainly used for a mobile product at present, but is expected to be developed into an application for an OLED television in the future. Some manufacturers have already begun marketing the OLED television.
A panel size of the OLED television is significantly large in comparison to that of the mobile product. Thus, it is expected that a demand for producing a larger and thinner glass sheet increases in the future.